The invention relates to short-range data communication.
Radio frequency identification (RFID) systems, for example, typically include a reader or interrogator, a transponder and a data processor. The reader may include an internal microcontroller, a transmitter, a receiver, and an antenna. The transponder is usually a passive device (having no power source) embedded in a card or key tag, and may include an antenna and a RFID application specific integrated circuit (ASIC). The interrogator transmits an electromagnetic wave defining a surveillance zone. When a transponder enters the zone, the electromagnetic energy from the interrogator begins to energize the ASIC in the transponder, which initializes and then broadcasts an identity signal.
A RFID system may use a low-energy, back-scattering technology that selectively reflects or back-scatters the electromagnetic energy from the transponder back to the interrogator. Receiving circuitry in the interrogator senses and decodes the back-scattered signal to determine the identity of the transponder. Such a system may be used to identify, track and/or locate people or objects.
In a typical application, when an acceptable identity signal has been received, an interrogator generates a signal to unlock a door for entry of the carrier of a key tag transponder. Another application uses button transponders attached to an article of clothing to communicate with an interrogator in a washing machine or the like. The button transponders communicate data to the interrogator that are used to alter the water temperature and/or the cleaning cycle for the clothing.
RFID systems typically offer a single communication path between a reader and the transponders, and have short read ranges between the interrogator and a transponder, which may be measured in centimeters. Greater ranges, very often the goal of RFID systems, require use of higher power levels and/or increased antenna size, and produce less confined radio frequency fields.